It is not known whether this site was upgraded to a commercial mine site. It would appear not, as it is not listed in any recent USDoE or USEPA literature. The ISL trial very clearly showed that there were many significant operational and environmental problems with sulphuric acid leaching chemistry. These include the mobilisation of extremely high levels of radioactive thorium, the buildup of mineral precipitates (such as gypsum), the mobilisation and buildup of many trace elements during leaching and the difficulties of groundwater quality restoration.
2 - DEQ is the Wyoming government department with the statutory responsibility, along with the US
4.8
Environmental Problems at Early Texan Sites
Texas has been the dominant producer of uranium from ISL mines for nearly 25 years. However, contrary to the industry view, independent monitoring of some of these facilities by the Texas Energy Alliance (TEA) has showed that there were many excursions, surface spills and breaches of Texan regulations. A review of their work is therefore considered quite important to note. The following reviews are based on TEA 1989a, 1989b, 1988, 1987a, 1987b & 1982.
Overview
In Texas, the level of background radiation is generally well below the national average for the United States. Although there are spots where significant levels of radon and radium occur in groundwater, the quality of groundwater surrounding a uranium deposit is generally free of the high contamination levels that exist within the ore zone. The TEA argued that the natural steady state conditions that exist prior to mining are arguably capable of containing the migration of radionuclides, such as uranium and radium.
Another significant problem identified by the TEA was that only 65% of the uranium was extracted during ammonia-based ISL, and 96% of the radioactivity remained within the ore zone. The reducing agents that existed before mining were oxidised during the ISL process, and thus significant potential remained for radionuclides to migrate free from the controlling influence of reducing agents that existed prior to ISL mining. The principal problem associated with the use of ammonia-based leaching solutions was that ammonia was adsorbed by the clays within the aquifer, and this bound ammonia is undetectable by standard groundwater monitoring techniques. One estimate suggested that after mining, approximately 2 tonnes of ammonia remained adsorbed within an aquifer zone only 12x12 metres in area.
The presence of hundreds, or sometimes thousands, of old exploration boreholes was identified as one of the key causes of excursions into the shallow groundwater systems of an ISL mine site. The TEA also note that the deeper groundwater systems below a mined aquifer were generally not allowed to be monitored, and significant questions regarding the escape of leaching solutions into these systems along old oil exploration wells or fault zones are simply unanswered.
Due to the alkaline solutions used, the radon levels were extremely high, with one value of 167,000 pCi/l noted. This radon was vented to the atmosphere. It was thought that the exposure of workers to radon progeny would be consequently high.
Another serious problem facing various ISL mines across Texas was the decommissioning stage. An ISL mine generates a significant volume of solid radioactive wastes, including pipes, machinery, buildings, pond liners, filters, salts, etc. There was simply not enough capacity within Texas to accept this volume of waste, and yet there was no comprehensive waste management program in place to accept and manage such radioactive wastes.
Although companies such as Wyoming Minerals confidently presented their technical ability to restore groundwater quality after ISL mining, with one quote suggesting it would only take “a few weeks”, by the late 1970’s to the early 1980’s they were admitting that “developments in restoration technology have not advanced as far as was hoped, and after several years experience in mining and restoration, we now have a more realistic understanding of the limitations of this technology”. “Original standards were known to be strict but were accepted with the expectation that the state-of-the-art would solve some problems and the standards could be renegotiated (especially the standard for NH4) in light of further experience and understanding”.
One advancement in restoration technology was the use of Reverse Osmosis (RO) to treat the groundwater before recirculation through the ore zone. Although RO could lower the ammonia levels from 100 mg/l to 32 mg/l, the dilemma was the production of a highly concentrated waste stream that would be disposed of down a deep injection well. The number of pore volumes of groundwater required was between 30 to 50, and thus the quantities of waste involved reached billions of litres. The restoration requirement for ammonia, however, was only 0.8 mg/l.
The regulators and companies, after amending the restoration requirements, argued that due to the slow movement of groundwater in the area the contaminants will not migrate any significant distance. They argued that it will take between 3,000 and 3,500 years for the ammonia to break down naturally, and given the average groundwater velocity of 0.3 metres per year, will only migrate a total of 1 km before returning to background. However, there was no evidence proving such mechanisms, and the companies were simply waiting for the problem to develop before addressing the fundamental questions concerning environmental impacts on the groundwater environment.
After ISL mining has been completed, the companies were required to plug or cap all monitoring wells. Thus there could be no long term monitoring of the migration of both the ammonia and the radioactivity. The companies could thus adopt a least-cost/walk away approach without serious commitment to the protection of groundwater quality in the region.